Environmental factors modify genetic susceptibility to many chronic diseases. Commensal microbiota profoundly influence physiologic responses in a number of organs and heavily contribute to inflammatory, neoplastic and possibly degenerative diseases. The NGRRC provides a resource for local, regional, national and international multidisciplinary investigators to explore the hypothesis that commensal bacteria fundamentally Influence normal physiologic processes in normal hosts and pathogenic inflammatory and neoplastic responses in genetically susceptible hosts. This unit provides a resource for broadly based investigators to examine physiologic and pathophysiologic differences in germ-free (sterile) vs. gnotobiotic (known life) vs. specific pathogen-free rodents of different genetic backgrounds, and to define the physiologic and pathophysiologic relevance of bacterial genes. The microbiota can be precisely manipulated by colonizing germ-free rodents with single or multiple commensal or pathogenic bacterial or fungal species, using isogenic wild type or genetically engineered bacterial strains. Specific aims: 1. Provide germ-free or selectively colonized wild type and mutant mice and rats or their tissues and cells to NIH-funded investigators. 2. Develop innovative techniques to efficiently derive germ-free breeding colonies of new strains of mice and rats for requesting investigators and for the molecular detection and identification of contaminating bacteria. 3. Support pilot studies for investigators with novel hypotheses to generate preliminary data for NIH grant applications. We provide a unique and essential resource for a large, diverse group of NIH-funded investigators to study the physiologic and pathophysiologic consequences of colonization by commensal bacteria, with particular emphasis on gene/environmental interactions in genetically altered mice (transgenic, knockout or spontaneously mutated) with altered physiology and disease phenotypes. In our initial 4 years of funding, the NGRRC has provided 4621 gnotobiotic mice and rats to 61 investigators in 35 institutions. 39 funded and 11 submitted grants by 32 investigators depend on gnotobiotic animals from the NGRRC. Unique features of our facility are 1) interaction with the UNC Mutant Mouse Regional Resource Center (MMRRC), 2) the experience of the applicant team, 3) innovation in embryo transfer and cryopreservation, 4) The option for onsite tissue collection by external investigators, 5) highly trained technical staff to collect tissues or isolate cells for requesting investigators.